1. Field of the Invention
The present invention relates to a system and method for energy recovery using the front wheel of a vehicle.
2. Discussion of the Related Art
Electric and hybrid powered vehicles offer a means of transportation that emit substantially no pollutants and produce little noise. These features are especially important at a time when such pollution has become a major concern. Although major advances have been made in electric and hybrid powered automobiles, the same cannot be said for two-wheeled and three-wheeled vehicles such as motorcycles, scooters, mopeds, and trikes, hereinafter referred to as “motorcycle(s)”.
Motorcycles have a wide variety of uses and the potential to positively impact society and the environment through reduction of congestion and pollution in addition to other benefits arising from their propagation. Gasoline burning versions of these vehicles are used for recreational purposes, as a main means for transportation in every day use, and even in competitive racing. One major concern with using electric motors in vehicle design is battery life and battery size, which impact vehicle power and range, especially on motorcycles where space to accommodate batteries is extremely limited.
Electric and hybrid powered vehicles rely on electricity from an on-board electricity storage source such as a battery, capacitor, or combination of both (hereinafter “electrical accumulator”). The most common electrical accumulator in use today is a battery, which must be recharged periodically, either during or after use. The most common means for recharging an electric vehicle's battery is by plugging it into an AC power outlet for a long period of time. For hybrid vehicles, charging may occur during use from power delivered by an on-board internal combustion engine. Battery size becomes a key issue as consumers are demanding that electric vehicles operate at extended ranges that require larger and thus heavier batteries that are more costly and are not conducive to small vehicles such as motorcycles.
For these and other reasons, historically motorcycles have involved the use of only gasoline powered internal combustion engines. These vehicles have generally been gasoline powered because they can be quickly refilled from ubiquitous filling stations, can generate substantial power for their weight, and are relatively inexpensive. Today's battery technology does not provide for long duration sufficient to make an electric two or three-wheeled vehicle competitive with its gasoline powered counterparts, and so manufacturers have been slow to produce electric motorcycles. These drawbacks, however, can be rectified by a system that is capable of producing substantial regeneration of the battery during use, such as during regenerative braking events, in order to recharge the battery and extend vehicle range for greater performance and consumer acceptance.
One approach to providing regeneration of a battery during use is by the use of a kinetic energy recovery system (“KERS system”), which is also known as a regenerative braking system or energy recovery system. Kinetic energy recovery has been developed for electrically powered four-wheel production and race vehicles, but the systems developed for four-wheel vehicles (hereinafter “cars”) are not able to be effectively utilized in motorcycles due to issues relating to size, weight, vehicle stability, and for additional and non-obvious reasons.
One way to construct a KERS system that is known in the art is to utilize a “wheel motor”, which is an electric motor installed inside the structure of one or more of a vehicle's wheels. A wheel motor provides regenerative braking torque that can be used to charge an on-board battery. One fundamental problem of wheel motors is they must be of a large enough capacity to harvest a meaningful amount of energy sufficient to justify their weight and cost. In one example analysis performed by the inventors, a racing motorcycle was instrumented with a data acquisition system and it was discovered that during heavy braking, an amount of energy equivalent to 150 horsepower was being converted to heat by the traditional friction braking system installed on the front wheel. To capture this energy for use in battery charging would require a 150 horsepower wheel motor to be installed inside the front wheel, which would weigh more than 100 lbs and be extremely expensive. Additionally, the effect of adding more than 100 lbs to the front wheel of a motorcycle would create an extremely unstable and dangerous vehicle dynamics situation, since steering, balance, wheel size, and unsprung weight are all degraded considerably, assuming the bulky 150 horsepower motor could even be packaged inside a front wheel in the first place. Accordingly, there is a need for a system with the lightest possible components located at the front wheel that can transmit significant energy away from the front wheel to be converted to electricity by a generating device located separately from the front wheel, such as inside the frame of the motorcycle.
The negative effects that wheel motors present to motorcycles can be partially mitigated in electric or hybrid cars. Typically, cars steer by using the two front wheels, giving more steering stability than the one-wheel steering found on motorcycles. Cars do not have to lean during cornering and being larger, weight is not as much of a concern for cars as it is for motorcycles, which rely on being nimble for safe handling especially during cornering on windy roads. During braking, cars spread the traction and heat rejection work over four wheels, and the rear wheels of a car typically handle more braking effort than does the rear wheel of a motorcycle. In one example, the braking proportion of a car may be 70% front wheels and 30% rear wheels. For a motorcycle, the braking loads may be more like 90% front and 10% rear, and it is not uncommon for the rear wheel to actually lift off of the pavement during heavy braking, which means the front wheel is handling 100% of the braking.
Cars may be designed with electric motors driving some or all of the wheels; either by the use of wheel motors inside the actual wheels, or by the mechanical coupling of a motor to a driven wheel. Whenever a motor is coupled to drive a particular wheel, it is convenient to use that same motor for regeneration simply by configuring the motor controller for that motor to initiate regenerative braking torque rather than forward propulsion torque with little or no additional structure required. A very large percentage of electric and hybrid cars available today use a front wheel drive powertrain, which greatly facilitates the use of regenerative braking in such vehicles. Yet despite the steady increase of manufacturer interest in electric cars and the ease with which they may deploy a KERS system on their front wheel drive designs, electric motorcycles are extremely rare, and almost none of those that have been built use any kind of regenerative braking systems. This is because conventional wisdom in the field of electric motorcycles holds that since the electric motor is mechanically coupled to drive the rear wheel (where there is little regenerative benefit under braking due to the light loading of the rear wheel as previously discussed) such systems are ineffective on a motorcycle. Research and analysis conducted by the inventors on the effectiveness of rear wheel KERS systems indicate that such a configuration can be expected to produce no more than 1 C of charge current in the best case scenario, whereas embodiments in accordance with the present invention can deliver more than 10 times that amount through the collection of energy from the front, non-driven wheel. To the knowledge of the inventors of this application, no one in the art of electric motorcycle design has even recognized and certainly not addressed the problem of how to recover the abundant energy available from the front wheel of a motorcycle under braking, which is otherwise wasted as heat. Another factor that has caused the electric motorcycle industry to ignore KERS systems is the very high crash danger arising from the use of rear wheel regeneration because applying any braking torque to a lightly loaded rear wheel, especially when leaning into a turn, easily locks up the wheel and causes rapid loss of traction and control.
Other KERS system constructions may be used such as via hydraulic accumulators or flywheel storage, but like wheel motors, each have drawbacks that render them inappropriate for motorcycle applications. Companies such as Eaton Corporation have successfully implemented KERS systems known by their trademark as Hydraulic Launch Assist (“HLA®”) for heavy commercial vehicles such as garbage trucks. During braking, a hydraulic pump/motor coupled to the drivetrain creates hydraulic pressure inside a large hydraulic accumulator that acts to compress a gas such as nitrogen. This stored pressure is later released as a fairly short burst during acceleration back to the hydraulic pump/motor and is known to improve the efficiency of such vehicles. The use of a high pressure accumulator sufficient to provide a meaningful KERS system benefit on a motorcycle, coupled with the inefficiencies inherent in this type of accumulator system make it impractical for a motorcycle. Similarly, the storage of braking energy in a flywheel has been successfully implemented by Porsche AG in their 911 GT3 R Hybrid racecar. Using a 40,000 RPM flywheel provided by Williams F1 and two 80 horsepower electric motors, Porsche has reported their KERS system equipped racecar delivering an average of 6.2 mpg during race conditions versus 5.6 mpg for their non-KERS system equipped racecar at the Nurburgring race track in April 2010. While this is a noteworthy improvement in fuel economy, the packaging and handling impact on a motorcycle with a 40,000 RPM flywheel mounted to it combined with the extreme cost, cooling requirements, and limited energy storage make flywheels impractical for motorcycles.
The use of a mechanical or hydraulic (non-accumulator hydraulic system) energy transfer system holds promise as the basis of an effective KERS system solution for a motorcycle so long as certain precautions are taken with respect to safety and vehicle dynamics. The application of gears, shafts, pumps and other such structures to the front wheel and suspension of a motorcycle presents a number of challenges as it is easy to upset the safe handling characteristics of a two or three-wheeled vehicle, which are more sensitive to such changes than are cars. Even with the safe design and installation of a mechanical or hydraulic KERS system, safety and vehicle dynamics are dependent on the careful actuation and precise control of the system during operation as disclosed in more detail herein below.
One recent development in the area of using mechanical gears and shafts on a dirt bike or bicycle are described in U.S. Pat. No. 6,505,699, and related U.S. Patent Application Publication No. 2009/0188738 and U.S. Pat. Nos. 6,439,592; 6,182,991; 6,161,854; 7,487,854; 7,328,766; and 6,161,855 issued to Steven J. Christini, et al. all of which are incorporated by reference herein. The system described in U.S. Pat. No. 6,505,699 is designed to transfer a limited percentage of available power from a standard gasoline burning internal combustion engine to the front wheel of a dirt bike at certain times during operation. In doing so, Christini has achieved a dirtbike that may be operated in either standard rear-wheel drive or in a two-wheel drive mode, as manually determined from a rider-operated lever, depending on available traction in the dirt. U.S. Pat. No. 6,505,699 does not disclose or provide any teaching on recovering energy from the front wheel for use in recharging batteries or for any other purpose, and actually precludes such energy transfer by the teaching of one-way freewheel sprag clutches in the front wheel that operate to allow the motor to drive the front wheel but do not allow the front wheel to back drive the motor for regeneration. Additionally, U.S. Pat. No. 6,505,699 does not even disclose implementation in an electric powered vehicle.
It is clear that manufacturers and inventors of electric motorcycles have failed to recognize and address the problem of recovering kinetic energy from the front wheel. Limited efforts have been made to implement rear wheel KERS systems, but the poor regeneration provided by the lightly loaded rear tire have led most to abandon the pursuit of on-board recharging altogether. Industry experts have been quoted as saying that KERS systems on a motorcycle are a waste of time. KTM Power Sports AG is one company to try rear wheel KERS system on a motorcycle. KTM is a well known manufacturer of motorcycles and also endeavors to race their motorcycles in various events around the world. KTM has substantial engineering and financial resources. KTM reported using a rear wheel KERS system in the 2008 Valencia Grand Prix race on a 125 cc two-stroke motorcycle that generated an additional 2.68 horsepower and was subsequently banned by race organizers.
Unfortunately, the limited battery capacities available in the current state of the art combined with the industry's failure to recognize or employ the front wheel as a source of significant recharging energy, has combined to relegate the fledgling electric motorcycle industry to novelty status with an uncertain future due to limited vehicle range and performance.
Accordingly, there is an urgent need for a regenerative braking system that can capture significant energy from the front wheel of a motorcycle, that is also lightweight, efficient in its energy transfer, easy to package, cost effective, and does not impede the maneuverability or safety of the KERS system equipped motorcycle.